Typical greenhouse growth of plants makes use of the natural energy provided by the sun. However, in some cases, for example depending on the geographical location of the greenhouse, the amount of light and/or heat must be adjusted for controlling the growth of the plants growing inside of the greenhouse, using for example heating/ventilation systems as well as artificial and supplemental lighting for increasing the quantity of light provided to the plants and light absorbent curtains for reducing the quantity of natural light provided to the plants.
Artificial and supplemental lighting in a greenhouse typically involves use of an illumination system for stimulating plant growth, possibly even improving the growth process in comparison to the sole use of natural light. Such an illumination system typically comprising a plurality of high power light sources. Different types of light sources, having different light spectrum and providing different effects on growth stimulation, may be included, such as light sources based on metal halide (MH) or high intensity discharge (HID) which includes high pressure sodium (HPS). Using metal halide based lighting typically promotes shorter, bushy growth; whereas high pressure sodium based lighting in comparison typically tend to produce taller and stretched plants.
Recently, much progress has been made in increasing the brightness of light emitting diodes (LEDs). As a result, LEDs have become sufficiently bright and inexpensive to serve also for artificial lighting in e.g. a greenhouse environment, additionally providing the possibility of emitting light with adjustable color (light spectrum). By mixing differently colored LEDs any number of colors can be generated. An adjustable color lighting system typically comprises a number of primary colors, for one example the three primaries red, green and blue. The color of the generated light is determined by the LEDs that are used, as well as by the mixing ratios. By using LEDs it is possible to decrease the energy consumption, a requirement that is well in line with the current environmental trend. Additionally, using LED based illumination system minimizes the amount of light source generated heat which is specifically suitable in an environment where temperature control is desirable.
An example of an LED based illumination system is disclosed in WO2008118080, comprising a light sensor communicatively coupled to a processor, where the processor implements a control algorithm for modulating and improving plant growth and attributes by adjusting the light emitted by the LEDs.
WO2008118080 shows a promising approach in relation to artificial lighting in a greenhouse environment providing the possibility to introduce plant specific light regimes, however, it would still be desirable to further optimize the artificial and/or supplemental light emitted by an illumination system, to be able to improve the predictability of the overall growth process of a plant including when and where to control of the amount of light to be received by the plants to achieve a desired end result, specifically taking into account the total energy consumption for growing the plant and possibility to plan the work-flow for harvesting the plants.